The subject invention generally relates to controlling energy losses in fluid translating devices and more particularly to controlling the motion of the respective pistons when they are not in use.
Fluid translating devices are well known in the art and may be in the form of a fluid pump or a fluid motor. Piston types of fluid translating devices are normally used in systems to provide high operating torques and/or pressures. They may be in the form of radial piston designs, axial piston designs, bent axis designs or other known designs. In either of the types, a plurality of pistons are used and they reciprocate in and out of respective piston bores. When it is desired to change the flow displacement within the fluid translating device, energy is wasted by having to move the respective pistons in and out of the piston bores. It has been known to inactivate all of the pistons during use in order to hold the pistons in a predetermined position so that energy may be saved when the fluid is not needed to do useful work. One example of such a system is illustrated in the brochure entitled xe2x80x9cWe can help you pump up performance on the road, off the road, and down the roadxe2x80x9d published by Deere Inc. in April 1988. In the brochure, it teaches subjecting the internal cavity with pressurized fluid that forces each of the pistons to retract into their respective piston bores when the fluid flow into their respective pressure chambers is shut off. The pressurized fluid in the internal cavity is effective to move the respective pistons into their piston bores but the pressurized fluid within the internal cavity induces extra leakage paths and also creates unwanted drag forces therein.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the present invention, a variable displacement fluid translating device is provided and comprises a housing, a rotating cam, a plurality of piston bores, a plurality of pistons, a plurality of pressure chambers and a valving arrangement. The housing has first and second inlet/outlet ports and defines a reference axis therethrough. The rotating cam is disposed in the housing along the reference axis and has a cam surface. The plurality of piston bores are defined in the housing about the reference axis and each bore of the plurality of piston bores has a bottom portion. The plurality of pistons are slideably disposed in the plurality of piston bores and are selectively in mating contact with the cam surface of the rotating cam. The plurality of pressure chambers are defined in the housing between the respective one of the plurality of pistons and the bottom portion of the respective ones of the plurality of piston bores. The valving arrangement is connected between selected pressure chambers of the plurality of pressure chambers and the respective first and second inlet/outlet ports. The valving arrangement is operative to selectively block fluid flow in and out of each pressure chamber to hold the respective piston at a predetermined position.
In another aspect of the present invention, a method is provided to control the relative position of respective ones of a plurality of pistons within a variable displacement fluid translating device. The method comprises the following steps: provide a housing having first and second inlet/outlet ports and a reference axis; provide a rotating cam having a cam surface in the housing along the reference axis; form a plurality of piston bores in the housing about the reference axis; provide a plurality of pistons in the plurality of piston bores that are slideably disposed in the respective piston bores and that are selectively in mating contact with the cam surface of the rotating cam; establish a plurality of pressure chambers between the respective one of the plurality of pistons and the respective ones of the plurality of piston bores; and provide a valving arrangement between selected pressure chamber of the plurality of pressure chambers and the respective first and second inlet/outlet ports. In the method each valving arrangement is operative to selectively block the fluid flow in and out of each pressure chamber to maintain the associated piston at a predetermined position.